Process for the production of a rotor, containing permanent magnets, of a synchronous machine, and rotor produced according to this process

ABSTRACT

The rotor has a core with an internal space. Permanent magnets are arranged on the core. These permanent magnets are surrounded by an outer cylinder, which is connected flush to closure disks which bear stub shafts. Channels run out from the internal space in the radial direction to the region of the permanent magnets. A resin mass is first introduced into the internal space. The rotor is thereafter heated and run up to centrifuging rotational speed. As a result, the molten resin mass flows through the channels to the region of the permanent magnets and fills up all the cavities present there and also cracks which form in the brittle permanent magnets on running up to speed. The resin mass hardens while the rotor is kept at centrifuging rotational speed. Each surface region of the permanent magnets is thus reliably protected against corrosion.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority under 35 U.S.C. § 119 to GermanPatent Application No. 100 60 121.9 filed on Dec. 4, 2000, the entirecontents of which are incorporated by reference herein. In addition,this application is a divisional application of U.S. patent applicationSer. No. 09/996,694 filed on Nov. 30, 2001, the entire contents of whichare incorporated by reference herein.

FIELD OF THE INVENTION

[0002] The present invention relates to the production of a rotor,containing permanent magnets, of a synchronous machine, which rotor hasa core of ferromagnetic steel, on which and connected to the core ofwhich are permanent magnets which in turn are surrounded by an outercylinder of a non-magnetizable steel, and which rotor has closure platesof a non-magnetizable steel with a stub shaft.

BACKGROUND OF THE INVENTION

[0003] In the operation of a permanent magnet excited synchronousmachine, the permanent magnets seated on the rotor are exposed toconsiderable centrifugal forces, with the consequence that they tend tocome loose from the rotor. Shrinking on a metallic cylinder over themagnets seated on the rotor is known. The permanent magnets, as is wellknown, consist of a brittle material, so that cracks and breaks arealready practically unavoidable when shrinking the cylinder on. Thesepermanent magnets moreover consist of a material which is verysusceptible to corrosion and have to be wholly surrounded by aprotective layer which is also durable during operation. The applicationof such protective layers on the one hand requires much work and on theother hand, in known constitutions, leaves broken places on thepermanent magnets, occurring on (a first) run-up to operating rotationalspeed, without any protection against corrosion. It is known that thepermanent magnets have to be ground to obtain correct dimensions, Thisgrinding also requires much work.

SUMMARY OF THE INVENTION

[0004] The invention has as its object to provide a process ofproduction of a permanent magnet excited synchronous machine, and arotor produced by this process, according to which the permanent magnetsare mounted hydrostatically, so to speak, and furthermore the permanentmagnets also have no unprotected surfaces even after sustainingfractures after first running up to operating speed.

[0005] The process according to the invention is distinguished in thatthe core is constituted with an internal space, and a resin mass isintroduced into the internal space and is supplied to the region of thepermanent magnets by centrifuging the rotor, a hardening of the resinmass then taking part in the said region. The rotor produced by theprocess according to the invention is characterized by a core offerromagnetic steel and an internal space extending axially, thepermanent magnets being arranged on the said core and being surroundedby an outer cylinder of non-magnetizable material, the said rotor havingclosure disks of non-magnetizable steel at both ends with stub shafts,which are positively connected to the core and at least frictionallyconnected to the outer cylinder, and that all the cavities in the regionof the permanent magnets are filled with a resin mass.

[0006] The advantages attained with the invention are in particular thatthe permanent magnets are completely surrounded by the resin mass andthus in actual fact are hydrostatically mounted, so that they aresecured against a displacement due to centrifugal forces; and that theresin mass is still flowable during the first running-up to speed, sothat it fills the cracked regions of the permanent magnets appearingduring this period, and covers the additionally resulting bare surfacesof the permanent magnets.

BRIEF DESCRIPTION OF THE DRAWING

[0007] Preferred embodiments of the invention are discussed in thefollowing description and illustrated in the accompanying drawings, inwhich:

[0008]FIG. 1 shows a longitudinal section through a first embodiment ofthe rotor according to the invention.

[0009]FIG. 2 shows a section along the line II-II of FIG. 1.

[0010]FIG. 3 shows a first embodiment of the connection between theouter cylinder and a closure disk of the rotor.

[0011]FIG. 4 shows a second embodiment of the connection between theouter cylinder and a closure disk of the rotor.

[0012]FIG. 5 shows a third embodiment of the connection between theouter cylinder and a closure disk of the rotor.

[0013]FIG. 6 shows, on an enlarged scale, a cross section through aportion of the rotor, in order to illustrate the filler strips.

[0014]FIG. 7 shows a longitudinal section, similar to that of FIG. 1,through a portion of a second embodiment of the rotor according to theinvention.

[0015]FIG. 8 shows a diagram of a slotted sheet of a sheet metal packetshown in FIG. 7.

[0016]FIG. 9 shows a schematic view of a portion of a rotor with a cage.

[0017]FIG. 10 shows a section along the line X-X of FIG. 9.

DETAILED DESCRIPTION OF THE INVENTION

[0018] The rotor of the first embodiment, shown in FIG. 1, has anintegrally constituted core 1 of a ferromagnetic material. Permanentmagnets 2 are arranged on the core 1. The permanent magnets are shown asone piece for the sake of clarity, but they can however also bearbitrarily divided. The permanent magnets 2 are surrounded by an outercylinder 3 of a metallic, non-magnetizable material. The outer cylinder3 can consist, for example, of high strength, cold-rolled, austeniticsteel, or of a high strength bronze which conducts electricity well,e.g., CuNi₃Si, to achieve the smallest electrical surface losses. Therotor ends on both sides with a closure disk 4 or 5 with a stub shaft 6or 7 which consists of non-magnetizable steel.

[0019] The core 1 has an internal space 8 constituted as an axialthrough bore, which serves as a storage space as will be described.Channels 27 run in a radial direction from the internal space 8 to theregion of the permanent magnets 2.

[0020] The core 1 furthermore has a polygonal recess 18 at both axialends. The closure disks 4 or 5 have a correspondingly shaped projection19. The core 1 is centered on the closure disks 4 or 5 by means of theseprojections 19 and recesses 18, the polygonal shape moreover serving forexcellent transmission of the torque of the core 1 to the closure disks4 or 5 and thus to the stub shafts 6 or 7. Instead of a centralprojection 19, there can be an arrangement of shear bolts 38 whichconnect the core 1 to the closure disks 4 or 5.

[0021]FIG. 2 shows a section through the rotor along the line II-II ofFIG. 1. It can be seen that the permanent magnets 2 seated on the core 1are encircled by the outer cylinder 3, and the core 1 has the internalspace 8. In a known manner, the rotor forms a north pole N and a southpole S in the 2-pole embodiment shown here by way of example. Lateral,magnetically neutral zones 37 are present, as is generally known. Fillerpieces 16 of a magnetizable or non-magnetizable material, according tothe desired magnetic salience, are inserted at these neutral zones 37,in the corresponding annular space portions between the outer cylinder 3and the core 1. The density of the material of these filler pieces 16 isadvantageously at least approximately equal to the density of thematerial of the permanent magnets 2, that is, the density of the fillerpieces 16 is advantageously similar to the density of the permanentmagnets 2.

[0022] For the assembly of the rotor, the outer cylinder 3, according toa variant, is shrunk onto the closure disks 4 or 5.

[0023] The final connection between the outer cylinder 3 and the closuredisks 4 or 5 takes place according to a first embodiment, which is shownin FIG. 3, by means of a tight peripheral weld seam 9. As will bedescribed hereinafter, the production of this tight peripheral weld seam9 takes place in two steps.

[0024] A further embodiment of the connection between the shrunk-onouter cylinder 3 and the closure disks is shown in FIG. 4.

[0025] The outer cylinder 3 of this embodiment has at both ends an innercircumferential groove 10. The respective closure disk 4 or 5 has acorresponding outer circumferential projection 11. Near this outercircumferential projection 11 is an outer circumferential groove 12 withan O-ring 13 inserted into it. If the outer cylinder 3 is shrunk ontothe respective closure disk 4 or 5, the respective outer circumferentialprojection 11 projects into the respective inner circumferential groove10. Furthermore, the respective O-ring 13 directly abuts the outercylinder 3.

[0026]FIG. 5 shows a further variant of the connection between the outercylinder 3 and the closure disk 4 or 5, in which no shrinking-on takesplace. The respective closure disk 4 or 5 has for this purpose acone-shaped portion 14 facing toward the rotor interior. Thiscone-shaped portion 14 ends in a shoulder portion 15 formed as a stop.In this embodiment, the closure disks 4, 5 are hydraulically pressed inover the cone-shaped portion 14 until they come to abut on the shoulderportion 15 in the outer cylinder 3.

[0027] Reference is made to FIG. 6 in addition to FIG. 5. The core 1shown in FIG. 6 has a polygonal circumferential surface. The dimensionsof the flat-surfaced surface portions 17 of the outer circumference ofthe core 1 correspond to the dimensions of the permanent magnets 2arranged on it. Thus the circumferential surface of the core 1 conformsto the contour of the permanent magnets 2, so that no large magnetic gapis present. Furthermore, excellent transmission of torque from thepermanent magnets 2 to the core 1 results from this polygonal shaping ofthe circumferential surface of the core.

[0028] Filler strips 20 of a dimensionally stable, preferably metallic,material are arranged between the individual permanent magnets 2. Thesefiller strips can be provided with a thin nonwoven covering for fittingpurposes, at least opposite the permanent magnets. Further filler strips21 are arranged between the permanent magnets 2 and the opposing innercircumferential regions of the outer cylinder 3. These further fillerstrips 21 consist of material which conducts well, e.g., Cu or Al.

[0029] Excellent fitting to the rectangular cross sectional shape of thepermanent magnets 2 is made possible by the filler strips 20, 21. Ifabsolutely necessary, only the faces of the permanent magnets 2 facingthe outer cylinder 3 are ground; for the rest, all the surfaces canremain unworked.

[0030] The further filler strips 21 are connected at their ends to aflexibly constituted ring 22 which conducts electricity well; see alsoFIG. 5. This ring 22 can consist of a braided wire or can be oflaminated construction. The connection of the further filler strips 21to the flexible ring 22 can take place by welding, e.g., spot welding.

[0031] These further filler strips 21 together with the ring 22 thusform a damping cage. During assembly of the rotor, these weldconnections are produced before the positioning and securing of theclosure disks 4, 5 on the outer cylinder 3.

[0032] In the embodiment shown in FIG. 7, the core, generally denoted bythe reference numeral 35, is embodied of stacked metal sheets 23. Thesemetal sheets 23 are arranged as a metal sheet packet on a centering tube24. The centering tube 24 has holes 25 running in a radial direction.The metal sheets 23 arranged in the neighborhood of these holes 25 havea longitudinal slot 26 and are stacked in a cyclically rotatedarrangement (see FIG. 8), so that passages from an internal space 36 ofthe centering tube 24 to the region of the permanent magnets 2 arepresent, analogous to the channels 27 of the first embodiment.

[0033] Instead of the centering tube 24, the metal sheets 23 can beperforated in order to be able to receive shear bolts 38. These shearbolts 38 can project in over the length of the metal sheet packet andinto the closure disks 4, 5, in order to transmit torque.

[0034] The embodiment with a core 35 of a metal sheet packet is aprecondition for an oscillating magnetization. However, this embodimenthas no damping cage according to that of the embodiment shown in FIGS. 5and 6.

[0035] The reference numeral 28 in FIG. 7 denotes, in each closure disk,periodically annularly positioned threaded holes to receive balancingscrews (not shown) for balancing the rotor. Alternatively, bores withdesired diameter and depth can be bored during balancing.

[0036] A yet further embodiment is shown in FIGS. 9 and 10. A cage 29with end rings 30 and longitudinal rods 31 is produced from a material(e.g., Cu, Al) which conducts well, and acts as an electrical dampingcage in the finished rotor. To assemble the rotor, this cage 29 ispushed into the outer cylinder 3. The individual permanent magnets 2 areinserted into the cage 29, which serves as a filling matrix, and areadhered to the outer cylinder with a provisional adhesive. Thereupon thecore 1 is pushed into the cage 29, and the closure disks 4, 5 are thenmounted.

[0037] Alternatively, the cage 29 with the permanent magnets 2 can firstbe arranged on the core 1 and then the outer cylinder 3 can be pushedover them.

[0038] The purpose of the transverse grooves 32 in the longitudinal rods31 will be explained hereinafter.

[0039] To complete the rotor according to the invention, a resin mass isintroduced into the internal space 8, serving as a storage space, of thecore 1, or in the embodiment according to FIG. 7, into the internalspace 36 of the centering tube 24. Such resin masses are generally knownand thus do not have to be described further. These resin masses canfurthermore contain fillers, e.g., an aluminum oxide powder.Advantageously, the resin mass is introduced in the form of a solid rod,as a so-called B-stage adhesive.

[0040] The rotor is then run up to speed and simultaneously heated,according to a predetermined time program. The program can includesteady state points at intermediate rotational speeds and intermediatetemperatures. The resin mass, now molten, thus penetrates through thechannels 27 in the core 1 or, in the embodiment of FIG. 7, through theholes 25 in the centering tube 24 and through the longitudinal slots 26in the relevant metal sheets 23, in a radially outward direction towardthe permanent magnets 2. The transverse grooves 32 described in FIG. 9serve to equalize the flow of the resin mass.

[0041] The resin mass flowing outward due to the centrifugal force fillsall the cavities present, and the permanent magnets 2 are completelysurrounded by the resin mass. Since it is known that cracks andfractures unavoidably occur in the brittle permanent magnets when therotor is first run up to speed, these regions also are reliably filledby the flowable resin mass.

[0042] The hardening of the resin mass takes place at the centrifugingspeed of the rotor. This speed is higher than the maximum rotationalspeed and is only applied during manufacture of the rotor.

[0043] The region of the inner level of the resin mass aftercentrifuging is shown in FIG. 1 by the arrows 33 and 34 and also by thedashed lines. The resin mass to be filed into the internal space isthereby determined.

[0044] Due to the hardening of the resin mass during centrifuging, theouter cylinder 3 remains prestressed at the later rotational speeds andwhen stationary.

[0045] It is to be mentioned that the peripheral weld seam 9 describedin connection with FIG. 3 is pre-welded only in a single pass before thedescribed course of hardening. The circumferential weld seam 9 iscompletely after-welded only after the course of hardening. The outercylinder 3 is seated on cooled clamp jaws (not shown) during the weldingprocess. The balancing of the rotor takes place at the threaded holes28, described in FIG. 7, after the course of hardening. The internalspace 8 in the core 1, or the internal space 36 of the centering tube25, can furthermore serve as a so-called heat pipe and be cooled via thestub shafts 6, 7 or by means of flanged-on heat exchangers. It is withinthe scope of the present invention that the rotor has a stub shaft atonly one side, and the other end remains free. The closure disk at thefree end remains for sealing purposes.

[0046] It is thus apparent that the permanent magnets are mountedhydrostatically, so to speak, and in particular that cracks occurringwhen the rotor is first run up to speed are filled with the molten resinmass, so that the permanent magnets are completely locked in from theambient atmosphere and thus are extremely corrosion-resistant.

[0047] The permanent magnets can be provided with insulating coatings inorder to prevent current paths to adjacent electrically conductingcomponents.

[0048] As an alternative mode of manufacture, prestressed flat bindingstrips can be placed around the permanent magnets and possible damperrods 21 before the installation of the outer cylinder 3. The permanentmagnets can then be magnetized in an oscillating manner. The rings 22are thereafter applied, without however removing the strips.Alternatively, the filler strips 20 can likewise consist of materialwhich conducts electricity well, and can be connected to the rings 22.

What is claimed is:
 1. Process for the production of a rotor of asynchronous machine, containing permanent magnets, the rotor having acore of ferromagnetic steel, on and connected to which core arepermanent magnets which in their turn are surrounded by an outercylinder of a non-magnetizable material, and which rotor has at bothaxial ends a closure disk of a non-magnetizable steel with a stub shaft,wherein the core is constituted with an internal space, the processcomprising: introducing a resin mass into the internal space; supplyingsaid resin mass to a region of the permanent magnets by centrifuging therotor; and hardening of the resin mass in the region of the permanentmagnets.
 2. Process according to claim 1, further comprising: heatingand simultaneously running up to a centrifuging speed the rotor with theintroduced resin mass, such that the resin mass is conducted outward,due to centrifugal force, from the internal space through radialchannels in the core, or from the internal space through holes andlongitudinal slots in the core, to the region of the permanent magnets,and the cavities present there are filled up; and maintaining the rotorat the centrifuging speed during the hardening of the resin mass. 3.Process according to claim 1, further comprising: arranging thepermanent magnets on the core by inserting the permanent magnets withplay into the outer cylinder; arranging at each end after theintroduction of the resin mass into the internal space the respectiveclosure disk, each closure disk consisting of non-magnetizable steelwith a stub shaft and the core centered in the closure disks; andconnecting the outer cylinder to the closure disks.
 4. Process accordingto claim 1, wherein the resin mass is introduced into the internal spacein the core in the form of a solid rod.
 5. Process according to claim 1,wherein the resin mass contains at least one filler.
 6. Processaccording to claim 1, wherein the outer cylinder is shrunk onto theclosure disks.
 7. Process according to claim 6, wherein the shrunk-onouter cylinder is connected flush to the closure disks by means of acircumferential weld seam.
 8. Process according to claim 7, wherein thecircumferential weld seam is pre-welded in only one pass before thecentrifuging of the resin and is only completely after-welded after thehardening of the resin.
 9. Process according to claim 6, wherein theouter cylinder is constituted at both ends with an inner circumferentialgroove and the closure disks are constituted with an outercircumferential projection and an adjacently arranged outercircumferential groove with an inserted O-ring, and the outer cylinderis shrunk onto the closure disks such that the respective outercircumferential projection of the closure disks projects into therespective inner circumferential groove, and the respective O-ring abutsthe outer cylinder flush.
 10. Process according to claim 1, wherein theclosure disks are constituted with a cone-shaped portion directed towardthe rotor interior, and are pressed into the outer cylinder, to connectwith it, as far as a stop.
 11. Process according to claim 1, whereinmagnetic neutral zones are present in annular space portions between thecore and the outer cylinder, which neutral zones contain no permanentmagnets, and the process further comprises inserting filler pieces intosaid annular space portions, the density of the material of the fillerpieces being at least approximately equal to the density of the materialof the permanent magnets.
 12. Process according to claim 1, furthercomprising inserting a filler strip between adjacent permanent magnets.13. Process according to claim 1, further comprising inserting a furtherfiller strip between the permanent magnets and the inner circumferentialregions of the outer cylinder lying opposite said permanent magnets. 14.Process according to claim 13, further comprising: forming a dampingcage by connecting the further filler strips at their ends to arespective flexibly constituted ring; arranging said further fillerstrips around the core; and installing the closure disks.
 15. Processaccording to claim 1, further comprising: producing a cage of anelectrically conductive material with end rings and axially-runninglongitudinal rods with transverse grooves for distributing the resin;inserting the permanent magnets into the cage; and pushing the cage withthe permanent magnets into the outer cylinder followed by adhering thepermanent magnets to the outer cylinder with a provisional adhesive andthereafter pushing the core into the cage, or pushing the core into thecage and thereafter pushing the outer cylinder over the cage with thepermanent magnets.
 16. Process according to claim 1, further comprisingstacking metal sheets on a centering tube to produce the core, thecentering tube having holes for the passage of resin mass arranged inthe internal space and the metal sheets having slots aligned with theholes for the further passage of the resin.
 17. Process according claim1, wherein the core is integral and is constituted with an internalspace, which internal space serves as a storage space for the resinmass, and from which internal space channels are constituted running ina radial direction toward the outside of the core.
 18. Process accordingto claim 1, wherein the core is constituted at both axial ends with apolygonal recess, each closure disk being constituted with a polygonalprojection corresponding to the recesses of the core, and the processfurther comprises inserting the projections into the recesses duringassembly of the rotor in order to form a positive connection for forcetransmission between the core and the closure disks.
 19. Processaccording to claim 1, wherein the core has an outer circumferentialsurface constituted of polygonal shape with many planar surfaceportions, the dimensions of each individual surface portion beingconformed to the dimensions of the permanent magnets so that a magneticgap formed between the core and the permanent magnets arranged on thesurface portions is minimized, and a predetermined transmission oftorque from the permanent magnets to the core is attained.
 20. Rotorcontaining permanent magnets, the rotor comprising: a core offerromagnetic steel; an internal space running axially; at least onepermanent magnet arranged on the core; an outer cylinder ofnon-magnetizable material surrounding the at least one permanent magnet;and closure disks of non-magnetizable steel, each closure disk having astub shaft and positively connected to the core and at leastfrictionally connected to the outer cylinder, wherein after interfusinga resin at least a plurality of the cavities in the region of thepermanent magnet are filled with the resin as far as the diameter of theinternal space.
 21. Rotor according to claim 20, wherein the outercylinder is shrunk onto the closure disks.
 22. Rotor according to claim21, wherein the shrunk-on outer cylinder is connected flush to theclosure disks by means of a circumferential weld seam.
 23. Rotoraccording to claim 21, wherein the outer cylinder has a circumferentialgroove at each end, and the closure disks have an outer circumferentialprojection and an adjacently arranged circumferential groove with aninserted O-ring, said outer circumferential projections projecting intothe respective inner circumferential groove and said O-ring abutting theouter cylinder flush.
 24. Rotor according to claim 20, wherein eachclosure disk has a cone-shaped portion directed toward the rotorinterior and has a shoulder portion serving as a stop, said closuredisks being pressed into the outer cylinder and abutting it with theshoulder portion.
 25. Rotor according to claim 20, further comprising: aplurality of annular space portions between the core and the outercylinder defining a plurality of magnetic neutral zones, said neutralzones containing no permanent magnets; and a plurality of filler piecesarranged in the annular portions, the filler pieces having a density atleast approximately the same as a density of the permanent magnets. 26.Rotor according to claim 20, further comprising a filler strip arrangedbetween adjacent permanent magnets.
 27. Rotor according to claim 20,further comprising a further filler strip arranged between the permanentmagnets and the inner circumferential regions of the outer cylinderopposite to the permanent magnets.
 28. Rotor according to claim 27,wherein the further filler strip consists of an electrically conductingmaterial and, for the formation of a damping cage, are connected attheir ends to a flexibly constituted ring within which the core isarranged.
 29. Rotor according to claim 20, further comprising a cage ofelectrically conducting end rings and longitudinal rods with transversegrooves for the distribution of the resin, the permanent magnets beinginserted into said cage.
 30. Rotor according to claim 20, wherein thecore is formed by a metal sheet packet comprising a plurality of metalsheets arranged on a centering tube, the centering tube having aplurality of holes, wherein the metal sheets have longitudinal slotsrunning in the radial direction and aligned with the holes.
 31. Rotoraccording to claim 20, wherein the core is integral and has an internalspace from which a plurality of channels run in a radial direction tothe outside of the core.
 32. Rotor according to claim 20, wherein, fortorque transmission from the core to the closure disks, the core has apolygonal recess at each axial end, and each closure disk has apolygonal projection projecting into the respective recess.
 33. Rotor,according to claim 20, wherein the core has a polygon-shaped outercircumferential surface, consisting of individual plane-surfaced surfaceportions, whereby the surface portions correspond to the dimensions ofthe permanent magnets abutting the same.
 34. Rotor according to claim20, wherein the core is formed by a metal sheet packet comprising aplurality of metal sheets and a plurality of shear bolts inserted at oneend into the metal sheets and at a second.